1. Field of the Invention
The present invention relates to outer coating substrates for electronic components, for example, piezoelectric oscillators, and piezoelectric resonant components including the outer coating substrates. In particular, the present invention relates to outer coating substrates for electronic components which are constituted by laminating various material layers, and piezoelectric resonant components using the outer coating substrates.
2. Description of the Related Art
In electronic components, for example, piezoelectric oscillators, outer coating substrates made of ceramics have been widely used to protect electronic component elements.
For example, a piezoelectric resonator 101 shown in FIG. 10 is disclosed in Japanese Unexamined Patent Application Publication No. 4-4604. In the piezoelectric resonator 101, outer coating substrates 103 and 104 are laminated on the top and bottom of an energy trap piezoelectric resonant element 102. The outer coating substrates 103 and 104 are made of alumina obtained by low temperature calcining. Ceramics, for example, alumina, is superior in strength. However, manufacturing costs are high due to high calcining temperatures. It is disclosed in Japanese Unexamined Patent Application Publication No. 4-4604 that the calcining temperatures are lowered to reduce the manufacturing costs.
On the other hand, a crystal oscillator shown in FIG. 11 is disclosed in Japanese Unexamined Patent Application Publication No. 9-208261. In this disclosure, the crystal oscillator 112 is sealed in a package composed of a base member 113 and a cap member 114. The base member 113 and the cap member 114 are made of a glass-ceramics composite so that calcining at a low temperature of about 800° C. to 1000° C. is described as being possible.
Furthermore, a composite layer ceramic component shown in FIG. 12 is disclosed in Japanese Unexamined Patent Application Publication No. 10-106880. In this disclosure, low dielectric constant layers 121 and 124 are arranged as outermost layers, and the low dielectric constant layers 121 and 124 are made of a mixed material of ceramic powder and amorphous glass. High dielectric constant layers 122 and 123 are arranged between the low dielectric constant layers 121 and 124. It is described that characteristics of capacitors, resonators, and other electronic components, which include conductor layers 125 and 126, are improved by the high dielectric constant layers 122 and 123.
The outer coating substrates 103 and 104 of the piezoelectric resonator described in Japanese Unexamined Patent Application Publication No. 4-4604 can be calcined at a relatively low temperature. However, the contraction rate during calcination is large. Therefore, it has been a problem that the dimensional precision of the outer coating substrates 103 and 104 is insufficient.
On the other hand, a glass-ceramics composite is used in the structure described in Japanese Unexamined Patent Application Publication No. 9-208261 and in Japanese Unexamined Patent Application Publication No. 10-106880. The glass-ceramics composite can be calcined at a low temperature. However, the contraction rate during calcination is large also, and the precision of substrate dimension has been insufficient.